The present invention relates to a device for suppressing engine knocks in an internal combustion engine, including in a motor vehicle.
In German Patent No. 34 204 65 is discussed a device for suppressing engine knocks in an internal combustion engine. As characterized, operating parameters of the internal combustion engine are acquired, and on the basis of these acquired operating parameters, in a control unit the respective manipulated variables for the processes to be controlled, such as, for example, ignition and injection, are determined. Thus, for example, on the basis of rpm and current load, the optimal ignition point is calculated.
As further characterized, moreover, a knock detector acquires the combustion noises of the individual cylinders. The signals of the knock detector are forwarded to a knock signal evaluation circuit, and there, after filtering out the background noise, they are compared with a reference level. If a knocking combustion is recognized, then for a knock suppression the ignition point, determined on the basis of rpm and load, in this cylinder is retarded, and thus away from the knock limit. After a predeterminable number of knock-free combustions, this modified ignition point is again led back step-by-step to the manipulated variable determined by the control apparatus. Since, given a cold engine, there may be no danger of knocking combustions, the knock control may be switched to active only after a predeterminable engine temperature has been reached, i.e., after warming up the internal combustion engine. Below this enable temperature, it is believed to be at least reasonably certain that no knocks can occur, because the thermal conditions in the combustion chamber do not allow this.
In certain systems, for the determination of the engine temperature, the cold water temperature or the gas entry temperature into the combustion chamber may be determined.
In German Published Patent Application No. 44 01 828 is discussed a method that enables a prediction that is as precise as possible, at the time of the calculation of the quantity of fuel to be metered, of the air charge of the cylinder into which the quantity of fuel is injected.
As characterized in German Published Patent Application No. 44 01 828, a future load signal is determined that represents the relative air charge to be expected. The future load signal is determined from a current main load signal, a current auxiliary load signal that runs in front of the current main load signal, and a crank angle interval. The crank angle interval can be predetermined dependent on the fuel preconditioning, expressed in time units or crank angle units, the duration of the fuel injection, and the calculation time. The inclusion of the crank angle interval has the advantage that the determination of the future load signal can be carried out or performed at the latest possible time, thereby achieving a high degree of precision.
It may be useful that the future load signal is determined using a lowpass filter whose filter constant can be predetermined dependent on load. The filter constant is read out from a first characteristic given an increasing load, and is read out from a second characteristic given a decreasing load. In this way, a predetermination of the air charge is possible that may be particularly economical in terms of computing time.
The auxiliary load signal is determined from the opening angle of the throttle valve, the rpm of the internal combustion engine, and an air quantity that flows to the throttle valve, through a bypass duct if necessary, and is corrected dependent on the temperature of the intake air and the barometric altitude.
Given small opening angles of the throttle valve, the auxiliary load signal can also be determined from the air mass, acquired using an air mass meter, which may result in a higher degree of precision in this operating range.
The main load signal can for example be determined from the measured intake pipe pressure and the rpm, from the air mass acquired using an air mass meter, or through filtering of the auxiliary load signal.
The method can be used both in non-stationary operation and also in stationary operation, since in the determination of the future load signal an auxiliary load signal matched to the main load signal can be used. The compensation value required for the compensation of the auxiliary load signal is determined through integration of the deviation between the main load signal and the filtered auxiliary load signal provided with the compensation value. The filtered auxiliary load signal is thereby produced by filtering the corrected auxiliary load signal.
In this method, the future load signal is used only for the determination of the quantity of fuel to be injected.
The problem is believed to be that given dynamic changes in load, spark ignition engines may exhibit an increased tendency to knock in comparison with stationary operation. An attempt may be made to counter this by issuing what may be referred to as an adaptive dynamic lead, i.e., an additional late adjustment of the ignition angle during the dynamic phase.
This additional dynamic lead is issued when the load gradient (i.e., the instantaneous velocity or instantaneous slope of the change of load), exceeds an applicable threshold value. The dynamic lead is then maintained over an applicable time, and is subsequently controlled to zero.
In the above approach, it is believed to be disadvantageous that the load gradient, as a differential, and therefore instantaneous, quantity, does not contain any information concerning the change of load that actually occurs during the overall, following, dynamic phase. This change of load results afterwards from the integration of the load gradient over time, which, however, may be too late for the determination of the dynamic lead.
That is, the issuing of the dynamic lead may depend only on how rapidly the load is changing at a point in time during the dynamic phase. Consequently, given a small, rapid change of load, the same dynamic lead may be issued as in the case of a large and likewise rapid change of load.
This is illustrated in FIG. 5. There, t designates time, tdyst designates the starting time of the dynamic phase, tdyena designates the end time of the dynamic phase for the case a, tdyenb designates the end time of the dynamic phase for the case b, rl designates the air charge, and drl designates the air charge gradient. In case a, a large, rapid change of air charge xcex94rla is present, and in case b a small, likewise rapid change of air charge xcex94rlb is present.
The thermal changes inside the engine, which influence the tendency to knock, may be much stronger in case a, and a greater dynamic lead should correspondingly take place. However, this may require that the integrated change of load that is to be expected be known already at the time of the triggering of the dynamic. Such information may not be available in the existing devices for suppressing engine knocks in an internal combustion engine.
The exemplary device according to the present invention is believed to have the advantage that it may enable a physically based, dynamically more precise determination of the dynamic lead, and thus a better suppression of knocking in the dynamic phase.
It is also believed that the adaptation algorithm may result in more precise adaptation values, and thus an improved dynamic behavior. The plausibility of the adaptation values can be better judged, thus simplifying the application method.
The exemplary embodiment involves determining the dynamic lead on the level of a predicted change of load signal or change of charge signal. It is noted that xe2x80x98load signalxe2x80x99 and xe2x80x98(air) charge signalxe2x80x99 are here used synonymously, since they are linked with one another via a xe2x80x9csimplexe2x80x9d proportionality factor.
For example, from the torque requirement, determined according to the accelerator pedal position and additional input quantities, a setpoint load or setpoint charge can be calculated. In this context, the actual load is adjusted to the setpoint load with a delay through corresponding positioning of the throttle valve and, if necessary, driving of the turbocharger. That is, at the instant of a large change in load required by the torque coordination, there is an immediate change to the actually existing charging in response thereto. However, with the predicted load difference, a measure for the change in load that is actually to be expected in the dynamic phase is already present at this point in time.
This means that in the dynamic case, instead of a signal indicating the instantaneous load gradient, the difference of a predicted load signal and an instantaneous load signal is used for the determination of the dynamic lead.
The magnitude of the dynamic lead is believed to be better adapted to the actual physical requirements, i.e., magnitude and velocity of the change of load. The issuing of unjustifiedly large dynamic leads, and, concomitant therewith, the worsening of the degree of efficiency and of the response characteristic of the engine, may be avoided in this way. Here, already-existing quantities of the motor controlling can be used.
In this way, what may be an essential cause of dynamic knocking, which may not optimally be taken into account by other ways of providing dynamic adaptation of the knock control, can be removed.
According to one exemplary embodiment, the correction device is constructed so that the dynamic lead is dependent on at least one acquired operating parameter, which may be the rpm.
According to another exemplary embodiment, the correction device is constructed so that it determines the predicted load difference by: detection of the load signal at a time located before the ignition point to be determined; prediction of a future load signal at a later time located before the ignition point to be determined; and formation of the difference of the future load signal and the load signal.
According to another exemplary embodiment, the correction device is constructed so that it predicts the future load signal from a current main load signal, a current auxiliary load signal that runs in front of the current main load signal, and a crank angle interval that can be predetermined dependent on the calculation time, expressed in time units or crank angle units.
According to another exemplary embodiment, the current auxiliary load signal can be determined from the opening angle of the throttle valve, the rpm of the internal combustion engine, and a quantity of air flowing, if necessary, through a bypass duct to the throttle valve and/or through additional bypass valves.
According to another exemplary embodiment, the current main load signal can be determined from the measured intake pipe pressure and the rpm, from the air mass acquired using an air mass meter, or through filtering of the current auxiliary load signal.
According to another exemplary embodiment, the correction device is constructed so that the prediction of the future load signal takes place with a taking into account of the camshaft control and/or the exhaust gas recirculation.
According to another exemplary embodiment, the dynamic phase detection device is constructed so that it acquires a dynamic phase of the internal combustion engine from the fact that the load gradient exceeds a predetermined threshold value.
According to another exemplary embodiment, the correction device is constructed so that it predicts the load difference at the time of the detection of a dynamic phase.
According to another exemplary embodiment, a knock detection device is provided that is constructed so that a knock monitoring can be carried out during the dynamic phase, and, dependent on the result of the knock monitoring, an adaptation of the dynamic lead can be carried out.
According to another exemplary embodiment, the correction device is constructed so that it compares the load difference predicted at the beginning of the dynamic phase with a load difference acquired at the end of the dynamic phase, and enables the adaptation only if the difference is smaller than a predetermined value.